[tests] migrate test_basic_actions as far as possible to `pytest`
[tests] migrate test_basic_actions as far as possible to `pytest`

There are some errors remaining, which probably relates to some
overlooked fixture overrides in `tests.frontend.conftest`.

Refs #580

agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft